Flow through percolation clusters: NMR velocity mapping and numerical simulation study - art. no. 041514

Citation
A. Klemm et al., Flow through percolation clusters: NMR velocity mapping and numerical simulation study - art. no. 041514, PHYS REV E, 6304(4), 2001, pp. 1514
Citations number
21
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physics
Journal title
PHYSICAL REVIEW E
ISSN journal
1063-651X → ACNP
Volume
6304
Issue
4
Year of publication
2001
Part
1
Database
ISI
SICI code
1063-651X(200104)6304:4<1514:FTPCNV>2.0.ZU;2-I
Abstract
Three- and (quasi-)two-dimensional percolation objects have been fabricated based on Monte Carlo generated templates. The object size was up to 12 cm (300 lattice sites) in each dimension. Random site, semicontinuous swiss-ch eese, and semicontinuous inverse swiss-cheese percolation models above the percolation threshold were considered. The water-filled pore space was inve stigated by nuclear magnetic resonance (NMR) imaging and, after exerting a pressure gradient, by NMR velocity mapping. The spatial resolutions of the fabrication process and the NMR experiments were 400 mum and better than 30 0 mum, respectively. The experimental velocity resolution was 60 mum/s. The fractal dimension, the correlation length, and the percolation probability can be evaluated both from the computer generated templates and the corres ponding NMR spin density maps. Based on velocity maps, the percolation back bones were determined. The fractal dimension of the backbones turned out to be smaller than that of the complete cluster. As a further relation of int erest, the volume-averaged velocity was calculated as a function of the pro be volume radius. In a certain scaling window, the resulting dependence can be represented by a power law, the exponent of which was not yet considere d in the theoretical literature. The experimental results favorably compare to computer simulations based on the finite-element method (FEM) or the fi nite-volume method (FVM). This demonstrates that NMR microimaging as well a s FEM/FVM simulations reliably reflect transport features in percolation cl usters.